Methods for detecting antimicrobial surface coatings using fluorescent indicators

ABSTRACT

Disclosed are methods for detecting a presence or absence of an antimicrobial surface coating including applying at least one detectable fluorophoric dye compound to a substrate, irradiating the surface of the substrate with ultraviolet radiation in the 100-415 nm wavelength range to excite the detectable fluorophoric dye compound, observing fluorescence of the excited fluorophoric dye compound, and determining the presence or absence of the antimicrobial surface coating based on the observed fluorescence. Further disclosed are antimicrobial surface coating solutions, methods for their application, and methods for confirming the presence and coverage of antimicrobial surface coatings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional patent application claims the benefit of U.S.Provisional Application No. 63/043,661 filed Jun. 24, 2020 and entitled“METHOD FOR DETECTION AND TAGGING OF ANTIMICROBIAL COATED SURFACES”, andU.S. Provisional Application No. 63/062,855 filed Aug. 7, 2020 andentitled “ANTIMICROBIAL COATING CONTAINING FLUORESCENT INDICATOR ANDCOATING DETECTION METHODS”, the disclosures of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present disclosure is directed generally to antimicrobials and moreparticularly to antimicrobial surface coatings and methods for detectinga presence or absence of an antimicrobial surface coating using afluorescent indicator.

BACKGROUND

It is well known that various surfaces can harbor microbes. It is alsowell known that contact with contaminated surfaces can spread infectiousagents such as bacteria and viruses. For example, high-contact interiorsurfaces in a conveyance such as a passenger aircraft have a highpotential to transfer microbes between passengers. While thesehigh-contact surfaces can be disinfected during regular cleanings,comprehensive cleaning and sterilization solutions can betime-consuming. Further, there remains the potential for microbetransfer between cleanings. This potential can be alleviated usingantimicrobial surface coatings. While effective, antimicrobial surfacecoatings can degrade and wear away over time and therefore must bechecked to ensure their continued presence and reapplied, as necessary.

Quaternary ammonium compounds (QACs) are commonly used in antimicrobialsurface coatings due to their ability to neutralize microbes. That sameability can also be used to bond anionic dyes, for instance bromophenolblue (BPB), to detect the presence of antimicrobial coatings via dyebonding and visual inspection. While effective, the process of bondingvisible dyes to surface coatings can permanently stain the surface undertest and are reliant on absorbance, which is not inherently sensitive.

Therefore, what is needed are methods for detecting the presence orabsence of antimicrobial surface coatings without the need forcomplicated procedures and without any negative effect on the cosmeticappearance of the coated surface, while having the sensitivity to detecteven monolayers of coating.

BRIEF SUMMARY

To achieve the foregoing and other advantages, in a first aspect thepresent disclosure provides a method for detecting the presence orabsence of an antimicrobial surface coating. In embodiments, the methodincludes providing a substrate to be tested, applying a detectablefluorophoric dye compound to a surface of the substrate, irradiating thesurface of the substrate with ultraviolet radiation in the 100-415 nmwavelength range to excite the detectable fluorophoric dye compound,observing fluorescence corresponding to the excited, detectablefluorophoric dye compound, and determining, based on the observedfluorescence, a presence or absence of an antimicrobial surface coating.

In some embodiments, the method may further include the step ofpre-treating the substrate with an antimicrobial surface coatingsolution comprising an antimicrobial component configured to covalentlybond to the substrate.

In some embodiments, the step of applying the detectable fluorophoricdye compound to the surface of the substrate may include the steps ofdepositing the detectable fluorophoric dye compound on the surface ofthe substrate, allowing the detectable fluorophoric dye compound tostand on the surface of the substrate for at least 30 seconds, removingexcess detectable fluorophoric dye compound, and drying the substrate.

In some embodiments, the detectable fluorophoric dye compound may beprovided as a water-based or alcohol-based solution.

In some embodiments, the substrate may be associated with a passengercabin of a conveyance, for instance an aircraft, train, subway, bus,automobile, or vessel.

In some embodiments, the substrate may be an element of a passengerseat, a passenger suite, a passenger amenity, a control unit, a closetor stowage/luggage bin, a lavatory, a self-serve bar or kiosk, or agalley.

In some embodiments, the substrate may be a mechanism for actuating anelement in a passenger cabin environment.

The present disclosure further provides a method of coating a substratewith an antimicrobial coating including a detectable fluorescentindicator. In embodiments, the method includes providing a substrate,providing an antimicrobial coating solution comprising an antimicrobialcomponent configured to covalently bond to a surface of the substrateand a detectable, water-soluble fluorescent indicator configured toabsorb ultraviolet radiation in the 100-415 nm wavelength range and emitradiation in the 100-1000 nm wavelength range, preferably in the 380-740nm wavelength range, applying the antimicrobial coating solution to thesurface of the substrate, and allowing the antimicrobial coatingsolution to dry on the surface of the substrate to form theantimicrobial coating.

In some embodiments, the method may further include the steps ofirradiating the surface of the antimicrobial coated substrate withultraviolet radiation in the 100-415 nm wavelength range to excite thedetectable fluorescent indicator, observing fluorescence correspondingto the excited detectable fluorescent indicator, and confirming, basedon the observed fluorescence, at least one of a presence and coverage ofthe antimicrobial surface coating.

In some embodiments, the step of allowing the antimicrobial solution todry on the surface of the substrate may include allowing theantimicrobial coating solution to stand on the surface of the substratefor a time duration of at least 6 hours.

In some embodiments, the method may further include the steps of rinsingand drying the surface of the antimicrobial coated substrate.

In some embodiments, the method may further include the step of, in theabsence of fluorescence or due to inadequate coverage, reapplying theantimicrobial coating solution to the surface of the substrate.

In some embodiments, the substrate may be associated with a passengercabin of a conveyance, for instance an aircraft.

In some embodiments, the substrate may be an element of a passengerseat, a passenger suite, a passenger amenity, a control unit, a closetor stowage/luggage bin, a lavatory, a self-serve bar or kiosk, or agalley and/or may correspond to a mechanism for actuating an element ina passenger cabin environment.

This brief summary is provided solely as an introduction to subjectmatter that is fully described in the detailed description andillustrated in the drawings. This brief summary should not be consideredto describe essential features nor be used to determine the scope of theclaims. Moreover, it is to be understood that both the foregoing summaryand the following detailed description are exemplary and explanatoryonly and are not necessarily restrictive of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. The use of the same reference numbers in different instances inthe description and the figures may indicate similar or identical items.Various embodiments or examples (“examples”) of the present disclosureare disclosed in the following detailed description and the accompanyingdrawings. The drawings are not necessarily to scale. In general,operations of disclosed processes may be performed in an arbitraryorder, unless otherwise provided in the claims. In the drawings:

FIG. 1 is a flowchart illustrating a method for applying anantimicrobial surface coating to a substrate and detecting the presenceof the coating using a detectable fluorescent indicator;

FIG. 2 is a flowchart illustrating a method for forming an antimicrobialsurface coating including a detectable fluorescent indicator, anddetecting the formed antimicrobial surface coating using the detectablefluorescent indicator; and

FIG. 3 illustrates schematically the implementation of the disclosedmethodologies to determine a presence or absence of an antimicrobialsurface coating.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail,it is to be understood that the embodiments are not limited in theirapplication to the details of construction and the arrangement of thecomponents or steps or methodologies set forth in the followingdescription or illustrated in the drawings. In the following detaileddescription of embodiments, numerous specific details may be set forthto provide a more thorough understanding of the disclosure. However, itwill be apparent to one of ordinary skill in the art having the benefitof the instant disclosure that the embodiments disclosed herein may bepracticed without some of these specific details. In other instances,well-known features may not be described in detail to avoidunnecessarily complicating the instant disclosure.

As used herein a letter following a reference numeral is intended toreference an embodiment of the feature or element that may be similar,but not necessarily identical, to a previously described element orfeature bearing the same reference numeral (e.g., 1, 1 a, 1 b). Suchshorthand notations are used for purposes of convenience only and shouldnot be construed to limit the disclosure in any way unless expresslystated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

In addition, use of “a” or “an” may be employed to describe elements andcomponents of embodiments disclosed herein. This is done merely forconvenience and “a” and “an” are intended to include “one” or “at leastone,” and the singular also includes the plural unless it is obviousthat it is meant otherwise.

Finally, as used herein any reference to “one embodiment” or “someembodiments” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment disclosed herein. The appearances of thephrase “in some embodiments” in various places in the specification arenot necessarily all referring to the same embodiment, and embodimentsmay include one or more of the features expressly described orinherently present herein, or any combination or sub-combination of twoor more such features, along with any other features which may notnecessarily be expressly described or inherently present in the instantdisclosure.

Broadly speaking, the present disclosure provides embodiments of methodsfor detecting antimicrobial surface coatings, detectable antimicrobialsurface coating solutions, and methods for forming detectableantimicrobial surface coatings.

FIG. 1 illustrates a first method 100 according to the presentdisclosure. In a step 102, a substrate is provided and an antimicrobialsurface coating solution is applied to at least a portion of a surfaceof the substrate via, for example, a conventional coating processincluding but not limited to electrostatic spray application, dipping,wiping, or other common application methods. In a step 104, theantimicrobial solution may stand on the surface of the substrate untildry to form the antimicrobial surface coating. In some embodiments, theantimicrobial coating solution may stand on the surface of the substratefor a predetermined time duration, for example, about 30 minutes toabout 6 hours to form the antimicrobial surface coating. Excess (e.g.,unbonded) antimicrobial surface coating solution may be removed in oneor more optional rinsing steps and the coated substrate may be dried inone or more optional drying steps.

In one or more of the embodiments of the present disclosure, thesubstrate may be any substrate type, for instance a high-contactsubstrate located in a passenger cabin of a conveyance such as anaircraft. Examples of substrates include, but are not limited to,synthetic or natural fabric surfaces, plastics, metals, composites andcomposite finishes, wood, glass, leather, and other non-cationicsubstrates. Substrate environments may include, but are not limited to,passenger cabins, crew quarters, lavatories, and galleys. Otherenvironments may include schools, hospitals, public buildings, etc. Inthe case of a passenger conveyance, the substrate may be an element of,for example, a passenger seat, a passenger suite, interior panels,luggage bins, doors, walls, passengers amenities, control panels,passenger service units, lavatory fixtures, galley equipment, andbeverage carts. In some embodiments, a substrate may be a mechanismoperable for manipulating an element, for example, a handle, lock,latch, switch, control panel, etc.

In one or more embodiments of the present disclosure, the antimicrobialcoating solution may include a quaternary ammonium compound (QACs,“quats) or other static/non-leachable compound (e.g.,silane-functionalized QACs, “SiQuat” or “silquat”) configured to attractnegatively-charged microorganisms to the surface where themicroorganisms are neutralized. To an extent, QACs and other such staticcompounds may covalently bond to the substrates to which they areapplied, resulting in sustainable layers of antimicrobial coatings thatmay persist for extended periods of time (e.g., 12 months or longer). Insome embodiments, the antimicrobial layers may be of no more thannanometer-level thickness, which means that while such antimicrobial orantiviral coatings are invisible under normal conditions, they may besusceptible to wear or erosion due to physical contact.

In a step 106, a tester, for instance a crewmember or maintenance staff,may perform a field assessment of the substrate under test by applying adetectable fluorophoric compound to the substrate surface. For example,the substrate under test (e.g., or a control portion thereof) may befully or partially immersed in one or more fluorophore-containingsolutions (e.g., a solution of 0.05 to 0.28 volume percent in water oralcohol). Alternatively or additionally, the fluorophore-containingsolution may be applied to the substrate by a process such as spraying,wiping, and via a pen-type applicator for direct application to thesurface. Alternatively, application of a detectable fluorophoriccompound may occur within minutes of application of the antimicrobialcoating, rather than during field assessment. In a step 108, thefluorophore-containing solution may stand on the surface of thesubstrate for a predetermined time duration, for example, about 30seconds up to about 5 minutes, more preferably about 30 seconds up toabout 6 hours or more. In a step 110, the substrate surface may berinsed to remove excess fluorophore-containing solution and then dried.In embodiments, fluorophoric solutions applied to the substrate undertest may bond to QACs or other static antimicrobial compounds. In someembodiments, fluorophores may be applied to a control portion of thesubstrate under test.

In a step 112, the substrate under test having the applied fluorophoricsolution is irradiated with ultraviolet radiation in the 100-415 nmwavelength range, more preferably in the 365-415 nm wavelength range, toexcite the at least one detectable fluorophoric dye compound. Forexample, the tester may apply long-wave ultraviolet (UV) light (e.g.,“blacklight”) to the treated substrate under test. In a step 114, thefluorescence corresponding to the excited fluorophoric dye compound isobserved. For example, while the applied fluorophores may beimperceptible under normal visible light (e.g., and therefore may notpresent as a “stain”), the fluorophores may fluoresce under UV light. Ina step 116, a presence or absence, or coverage, of the antimicrobialsurface coating is determined based on the observed fluorescence.

For example, areas of the substrate under test where the fluorophoreshave bonded to antimicrobial QACs fluoresce and therefore are clearlyvisible under UV light, indicating areas where the antimicrobial coatingis present. Similarly, a lack of fluorescence under UV light indicatesthe absence of an antimicrobial surface coating, for example, attenuatedby wear or erosion. In an optional additional step 118, the substrateunder test may be flagged for further action, for instance reapplicationof the antimicrobial surface coating, servicing, or replacement of theassociated substrate, element or component. In an optional step 120, thesubstrate under test may be washed with an aqueous solution containingsufficient concentrations of cationic species, such ascetyltrimethylammonium chloride or ammonium bicarbonate, to remove thedetectable fluorophoric dye compound to ‘reactivate’ the antimicrobialproperties of the underlying QACs or coatings.

In embodiments, the detectable fluorophoric dye compounds may be anionicdye compounds capable of bonding to QACs or other static antimicrobialcoatings, e.g., via sulfonate or carboxylic acid functional groups. Forexample, anionic dye compounds of λ_(ex)<500 nm and λ_(em)>400 nm may beideally invisible under normal visible light and fluoresce under UVlight (e.g., Tetrasodium4,4′-bis[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulphonatoanilino)-1,3,5-triazin-2-yl]amino]stilbene-2,2′-disulphonate],Disodium;5-[[4-anilino-6-[2-hydroxyethyl(methyl)amino]-1,3,5-triazin-2-yl]amino]-2-[2-[4-[[4-anilino-6-[2-hydroxyethyl(methyl)amino]-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate,Disodium4,4′-bis(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2′-stilbenedisulfonate,Disodium;5-[[4-(2-methylanilino)-6-morpholin-4-yl-1,3,5-triazin-2-yl]amino]-2-[2-[4-[[4-(2-methylanilino)-6-morpholin-4-yl-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate,Hexasodium;2-[[4-[(3-amino-3-oxopropyl)-(2-hydroxyethyl)amino]-6-[4-[2-[4-[[4-[(3-amino-3-oxopropyl)-(2-hydroxyethyl)amino]-6-(2,5-disulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]-3-sulfonatoanilino]-1,3,5-triazin-2-yl]amino]benzene-1,4-disulfonate,and related, as well as fluorescein-SA, Lucifer yellow, sulforhodamine-Bor sulforhodamine-101, pyranine, HPTS or HPTS(Lys)₃, MPTS, CTR, TSPP,TCPP, PTCA).

While the first method 100 is disclosed including both coating formationsteps coating detection/identification steps, it is envisioned andintended that the detection/identification steps can be practiced alonein the case of a substrate under test considered to already include anantimicrobial surface coating or a substrate under in which the presenceor absence of an antimicrobial surface coating is unknown. For instance,the detection steps can be practiced alone to determine antimicrobialcoating presence, coverage area, wear, etc., for the purpose ofdetermining the need for coating, recoating, spot-coating, replacement,etc. Further, the recited rinsing, washing and drying steps can beoptional or additional rinsing, washing and drying steps can beperformed. Coating application, dye compound application, rinsing,washing and drying procedures may vary depending on the substrate type,coating type, fluorophoric dye compound type, substrate location, andtesting environment, among other factors. The foregoing is applicable tothe recited method 100 and methods discussed further below.

FIG. 2 illustrates a second method 200 according to the presentdisclosure. Broadly speaking, the second method 200 includes the stepsof preparing an antimicrobial surface coating solution including adetectable fluorescent indicator component, coating a substrate with theprepared solution to form an antimicrobial surface coating, anddetecting the presence or absence of the applied antimicrobial surfacecoating. In some embodiments, the antimicrobial surface coating solutionmay include an antimicrobial component and a detectable, water-solublefluorescent indicator provided as a mixture to be coated on a substrateto impart antimicrobial properties to the coated substrate. In someembodiments, the solution may be a water-based or alcohol-basedsolution.

In a step 202, an antimicrobial surface coating solution is preparedincluding at least a quaternary ammonium compound or otherstatic/non-leachable compound and a detectable fluorescent indicator. Insome embodiments, fluorescent indicators according to the presentdisclosure may include any fluorescent compound capable of absorption inthe UV spectrum and emission in the visible spectrum. For example, thefluorescent compound may absorb radiation in the 100-415 nm wavelengthrange, more preferably in the 300-415 nm wavelength range, and mostpreferably in the 365-415 nm wavelength range, and emit radiation in the100-1000 nm wavelength range, more preferably emit visible light in the380-740 nm wavelength range. Suitable fluorescent compounds may betransparent in the presence of visible light and uncolored so as not toalter the color and/or transparency of the coating. Suitable fluorescentcompounds can include, but are not limited to, commercially availablefluorescent dyes, pigments, colorants and brighteners. A specific,non-limiting example of a suitable fluorescent compound can include5-[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-[(E)-2-[4-[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-1,3,5-triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate.

In a step 204, the prepared solution is applied to the predeterminedsubstrate and allowed to stand on the surface of the substrate until dryto form the antimicrobial surface coating. In some embodiments, theantimicrobial coating solution may be allowed to stand on the surface ofthe substrate for a predetermined time duration, for example, at leastabout 6 hours to form the antimicrobial surface coating. In an optionalstep 206, the coated substrate may be rinsed or wiped to remove excesssurface coating solution and subsequently dried.

In a step 208, the substrate under test having the formed surfacecoating is irradiated with ultraviolet radiation, for example, in the100-415 nm wavelength range, more preferably in the 365-415 nmwavelength range, to excite the detectable fluorescent indicator. Forexample, UV light may be directed to the substrate under test. In a step210, the fluorescence corresponding to the excited fluorescent indicatoris observed. In a step 212, a presence or absence, or coating coverage,of the antimicrobial surface coating is determined based on the observedfluorescence. For example, areas of the substrate that fluoresce areindicative of bonded antimicrobial surface coating, while areas of thesubstrate that do not fluorescence are indicative of uncoated substrate.

In some embodiments, the determination step 212 may include comparingthe intensity of fluoresce to a predetermined threshold value and/orcompared to a control area known to be coated or known to lack acoating. In some embodiments, intensity level data for a particularsubstrate may be saved for comparison against future data to track wearand/or coating performance. In some embodiments, the methods disclosedherein can be used to determine the level of coating wear between areasof a substrate by comparing the level of fluorescent intensity betweendifferent predetermined areas. For example, obtained data can be used todetermine frequent touchpoints that may require more frequent recoating,more robust coating, and/or additional coating layers. In an optionaladditional step 214, the substrate under test may be flagged for furtheraction, for instance reapplication of antimicrobial surface coating,servicing or replacement of the associated substrate, element orcomponent.

Methods according to the present disclosure can be used to verify thepresence or absence of an antimicrobial coating, for example, to verifythe application and quality of the coating during manufacturing, and/ordetect wear in the coating during service. In some embodiments, themethod includes providing a substrate coated with an antimicrobialsurface coating containing a fluorescent indicator, exposing the coatedsubstrate to UV light to excite the fluorescent indicator, and observingthe presence or absence of fluorescence to detect coating presence andwear. In further embodiments, the method may include measuring theintensity of fluorescence across a coated substrate exposed to UV lightand comparing the measured intensity to predefined threshold valuescorresponding to predefined wear indicators. Collected data may beanalyzed to determine coating performance, compare performance betweensubstrates, measure usage and wear, etc.

FIG. 3 shows schematically a substrate 300 under test, a detectablefluorescent indicator 302 (e.g., provided as an applied fluorophoriccompound according to the first method 100 or as a component of theformed antimicrobial surface coating according to the second method200), application of the appropriate radiation 304 to be absorbed by thefluorescent indicator 302, and emission of light in the visible spectrum306 indicating the presence of an antimicrobial surface coating.

Antimicrobial surface coatings according to the present disclosure findwidespread application in the field of antimicrobials and may be used tosurface treat any substrate benefitting from the advantages of anantimicrobial surface coating.

It is to be understood that embodiments of the methods disclosed hereinmay include one or more of the steps described herein. Further, suchsteps may be carried out in any desired order and two or more of thesteps may be carried out simultaneously with one another. Two or more ofthe steps disclosed herein may be combined in a single step, and in someembodiments, one or more of the steps may be carried out as two or moresub-steps. Further, other steps or sub-steps may be carried in additionto, or as substitutes to one or more of the steps disclosed herein.

What is claimed is:
 1. A method for detecting a presence or an absenceof an antimicrobial surface coating, comprising the steps of: providinga substrate; pre-treating the substrate with an antimicrobial surfacecoating solution comprising an antimicrobial component configured tocovalently bond to the substrate, wherein the antimicrobial surfacecoating solution does not comprise a detectable fluorophoric dyecompound; separately applying a detectable fluorophoric dye compound toa surface of the substrate at a time after the step of pre-treating thesubstrate; irradiating the surface of the substrate with ultravioletradiation in a 100-415 nm wavelength range to excite the detectablefluorophoric dye compound; observing fluorescence corresponding to theexcited detectable fluorophoric dye compound; and determining, based onthe observed fluorescence, the presence or the absence of theantimicrobial surface coating; wherein the determining step comprisesobtaining fluorescence intensity data and comparing the obtainedfluorescence intensity data to at least one of predetermined thresholdintensity data and intensity data of a control area of the substrateknown to be coated with an antimicrobial surface coating or known tolack an antimicrobial surface coating.
 2. The method according to claim1, wherein the step of applying the detectable fluorophoric dye compoundto the surface of the substrate comprises: depositing the detectablefluorophoric dye compound on the surface of the substrate; allowing thedetectable fluorophoric dye compound to stand on the surface of thesubstrate for a predetermined time duration; removing excess depositeddetectable fluorophoric dye compound from the surface of the substrate;and drying the surface of the substrate.
 3. The method according toclaim 1, wherein the detectable fluorophoric dye compound is provided ina water-based or alcohol-based solution.
 4. The method according toclaim 1, wherein the substrate is located in a passenger cabin of aconveyance.
 5. The method according to claim 4, wherein the substrate isan element of a passenger seat, a passenger suite, a passenger amenity,a control unit, a stowage/luggage bin, a self-service bar or kiosk, alavatory, or a galley.
 6. The method according to claim 4, wherein thesubstrate is part of a mechanism for actuating an element in a passengercabin environment.